1. Technical Field
The present invention relates to an offset correction circuit for correcting an offset in an output of a variable gain amplifier.
2. Background Art
Hitherto, direct conversion radio receivers for converting a received signal directly into a baseband signal are known. Also called a zero-IF system, the direct conversion system has an IF (intermediate frequency) frequency of 0 Hz. Therefore, the spectrum of the IF signal has a distribution close to DC. For this reason, the IF section circuit basically requires DC coupling.
When the IF section circuit is DC coupled, DC offset becomes a problem. Namely, this is because the DC offset of the IF signal is amplified by an amplifier and sent to a subsequent stage resulting in an operating voltage range of the circuit being exceeded.
Therefore, it is necessary to detect the offset of the IF signal and cancel the offset. Patent document 1 discloses a specific configuration example.    Patent document 1: Japanese Patent Laid-Open Publication No. 2004-172693